1. Field of the Invention
This invention relates to an interference device, a position detecting device, a positioning device and an information recording apparatus using the same. This invention can be applied particularly well to a position detecting device for detecting the positional fluctuation of an object in non-contact such as an interference length measuring device for an object like a hard disc drive magnetic head, a positioning device and a manufacturing apparatus for a hard disc drive device (hereinafter referred to as HDD) used in a computer utilizing the same, and above all, an apparatus for writing a servo track signal into a hard disc in the HDD.
2. Related Background Art
FIG. 1A of the accompanying drawings shows an illustration of an apparatus for writing a servo track signal into a hard disc in the HDD according to the conventional art.
In FIG. 1A, HDD designates a hard disc drive device, HD denotes hard discs, SLID designates a slider, ARM1 denotes a magnetic head arm, VCM designates a voice coil motor, OHD denotes the spindle of the hard discs HD, and O designates the rotary shaft of the magnetic head arm ARM1.
A magnetic recording medium is deposited by evaporation on the surface of each hard disc. The hard discs HD are normally rotated as a unit at a high speed about the spindle OHD, and a magnetic head is disposed in proximity to the surface of each hard disc HD. The magnetic head is incorporated in the portion of a substantially rectangular parallelopiped called the slider SLID mounted on the tip end of each arm portion of the magnetic head arm ARM1 having the center of rotation O outside the hard discs HD, and is relatively movable substantially in a radial direction on the hard discs HD by rotatively driving the arm ARM1 by the voice coil motor VCM.
Consequently, magnetic information can be written or read at any position (track) on the surfaces of the hard discs by the rotated hard discs HD and the arcuately moved magnetic head.
Now, a magnetic recording system onto the surface of the hard disc is such that each hard disc is splitted into a plurality of circular ring-shaped tracks of different radii concentric with the center of rotation OHD of the hard discs, and further each of the circular ring-shaped tracks in turn is splitted into a plurality of arcs and finally, magnetic information is recorded and reproduced on the plurality of arcuate areas time-serially along the circumferential direction.
Now, as the recent tendency, an increase in the recording capacity of the hard disc is required and there is a desire for the higher density of recorded information onto the hard disc. As means for the higher density of recorded information onto the hard disc, it is effective to narrow the width of the tracks splitted into concentric circles and improve the recording density in the radial direction.
The recording density in the radial direction is expressed by track density TPI (track/inch) per length of an inch, and at present it is of the order of 10000 TPI. This means that the track interval is about 3 xcexc. To form such a minute track pitch, it is necessary to position the magnetic head at resolving power (0.05 xcexc) of about {fraction (1/50)} of the track width in the radial direction of the hard disc HD and write a servo track signal in advance into the hard disc. The important technique here is to successively write servo track signals into the hard disc while effecting positioning of high resolving power within a short time.
PROD designates a push rod, ARM2 denotes an arm for the push rod PROD, MO designates a positioning control motor, RE denotes a rotary encoder for detecting the amount of rotation of the rotary shaft of the motor MO, SP designates a signal processor for analyzing the detection output from the rotary encoder RE, and producing a positioning command signal to the servo track signal writing-in position of the magnetic head, and MD denotes a motor driver for driving the motor MO by the command signal of the signal processor SP. These together form a rotary positioner RTP.
According to the conventional art, as shown in FIG. 1A, the cylindrical surface of the push rod PROD was pushed against the side of the magnetic head arm ARM1 (the arm portion for the magnetic head for the underside of the lowermost hard disc), and the arm ARM2 was rotated to thereby sequentially finely feed and position the magnetic head arm through the push rod PROD while taking feedback control by the system of the rotary encoder RE, the signal processor SP and the motor driver MD, and servo track signals from a signal generator SG were successively written in from the magnetic head. In order to ensure the contact at this time, some electric current was usually supplied to the voice coil motor VCM and the push rod PROD was also pushed from the head arm ARM1 side.
Recently, supposing more highly accurate positioning, a non-contact method of highly accurate measuring the movement of the magnetic head arm by optical means has been desired without adopting a system for mechanically pushing the magnetic head arm in which the vibration by the rotation or the like of the hard disc may be transmitted to the motor MO. FIG. 1B of the accompanying drawings shows an example of such an apparatus.
In FIG. 1B, HeNe designates a laser light source, M1 and M2 denote mirrors, BS designates a beam splitter, CC denotes a retroreflector such as a corner cube provided on the magnetic head arm ARM1, and PD designates a light receiving element.
In this apparatus, the laser light source HeNe, the mirrors M1 and M2, the beam splitter BS and the retroreflector CC together constitute a Michelson type interferometer, and the interference light of light beams L1 and L2 which have passed the retroreflector CC and the mirrors M1 and M2, respectively, is detected by the light receiving element PD to thereby obtain the positional information of the magnetic head arm ARM1. On the basis of the obtained detection signal, a signal processor SP produces a command and controls an electric current flowing from a voice coil motor driver VCMD to a voice coil motor VCM to thereby directly move the magnetic head arm and provide appropriate control.
In such an apparatus, however, it is necessary to place the retroreflector CC such as a corner cube on the magnetic head arm, and this is liable to lead to the problem of troubles such as the securement of space and the mounting and dismounting of the retroreflector, and the aggravation of the control characteristic by an increase in weight.
In view of the above-described examples of the conventional art, the present invention has as an object thereof to provide a position detecting device and a positioning device capable of detecting the position of an object and position the object in non-contact at high reliability and with high accuracy and high resolving power, an interference device making the same realizable and an information recording apparatus using the same.
Other objects of the present invention will become apparent from the following description of some embodiments of the invention.